This invention relates to an image sensor, for example for use in a facsimile machine or document scanner, and more particularly in which a light source for illuminating an image to be sensed is integrated into the structure of the image sensor.
Conventionally, an image scanner or facsimile machine comprises a light source, an image sensor array and an optical system for forming an image of an original on the image sensor. To reduce the overall size of these components it is also known to incorporate an electroluminescent light emitting element and a close contact image sensor as a single unit.
For example, JP-59-028756 discloses an optical sensor in which a light emitting plate is attached to one side of a substrate, and a photodetecting element is attached to the other side of the substrate. The light emitting plate has openings aligned with the photodetecting elements, enabling the passage of light to the detecting elements after reflection by the document to be imaged. This system suffers from the drawback that the optical arrangement does not provide a significant depth of focus for the document to be imaged, and fibre plates incorporated into the substrate and associated with each detecting element increase the cost of the optical sensor arrangement.
According to the present invention, there is provided an image sensor comprising an image capturing device for capturing an image on an imaging plane of the device, and a lens arrangement, the lens arrangement being positioned between an area to be imaged and the imaging plane, the lens arrangement comprising one or more arrays of spaced apart lens elements each for transmitting light from a portion of the area to be imaged to a portion of the imaging plane, the image sensor further comprising light emitting means disposed between the area to be imaged and the imaging plane and for illuminating the area to be imaged, the light emitting means being disposed in or over the spacing between the lens elements.
The use of a lens arrangement enables focusing of the area to be imaged, so that a document to be scanned may be positioned within a selected range, corresponding to the depth of focus of the lens arrangement. Positioning the light emitting means between the lens elements, or over the spacing between the lens elements, enables a compact arrangement for the complete optical system.
Preferably, the lens elements are microlenses, and there may be provided more than one microlens array, arranged so that each microlens in one array is on the same optical axis as a corresponding microlens in each other array. The lens arrangement preferably transmits a non-inverted image of the area to be imaged to the imaging plane.
Preferably, a sufficient distance is provided between the lens arrangement and the area to be imaged, to enable spreading of the light produced by the light emitting means before illumination of the area to be imaged.
The image capturing device preferably comprises a plurality of image sensing pixels, and each lens element is associated with a sub-array of one or more pixels. Preferably, each lens element is associated with a plurality of pixels.
The range of angles from which light can be received by each lens element will dictate the possible spacing between lens elements, and this spacing is arranged to be sufficient to enable an appropriate light emitting means to be designed.
The light emitting means may comprise discrete light emitting portions in or over the spacing between the lens elements. It is preferable for sufficient illumination of the area to be imaged to be possible from a proportion of the light emitting portions. Preferably, each light emitting portion is then selected from the group comprising red, green and blue light sources. The light emitting portions may comprise strips of electroluminescent light emitting material extending between the lens elements of one array. The strips may be arranged in a repeating sequence of the three colours. This enables the area to be imaged to be illuminated with a selected colour by activating the appropriate light emitting strips, and the spreading within the space between the lens arrangement and the area to be imaged enables a uniformly illuminated colour image to be recorded.
Alteratively, the light emitting means may comprise a light source arranged at a peripheral edge of the lens arrangement, and light deflecting portions arranged in or over the spacing between lens elements. The light deflecting portions may then comprise reflecting or diffracting elements.